1. Field of the Invention
The disclosed embodiments of the present invention relate to a defect diagnosis method, and more particularly, to a multiple defect diagnosis method which is applicable to a multiple defect case.
2. Description of the Prior Art
To fix yield problems in IC manufacturing, identifying root causes of systematic defects is critical. Physical failure analysis (PFA) is conducted on selected dies to understand defect mechanisms. Since PFA is a time-consuming and expensive process, the selection of dies should be carefully guided by systematic defect diagnosis. In recent studies, many dies have been discovered which have multiple defects; this issue therefore cannot be ignored in systematic defect diagnosis.
There are three main categories of multiple defect diagnosis. The first category uses covering-based methods. Multiple defect diagnosis is modeled as a minimum set covering problem, wherein a minimum set of faults is selected to cover all test failures of a pattern. A fault covers a pattern if simulation failures of the fault are exactly the same as test failures of the pattern. Simulation failures (SF) are results of fault simulation, while test failures (TF) are responses from automated test equipment (ATE).
The second category incrementally finds a fault at a time in order to correct a circuit. These techniques select a fault iteratively and update the SF of the circuit which is obtained by multiple fault simulation. The selection of faults continues until the SF of the circuit and the TF match. These techniques require many iterations of multiple fault simulation, which is time-consuming.
The last category generates diagnostic patterns to distinguish faults by different responses. Although the ease of diagnosis and resolution can be improved by using diagnostic patterns, the use of many iterations of testing is too expensive for production ICs.
In light of the above, there is an urgent need for a novel multiple defect diagnosis method which can improve the above issues.